Value update in hashmap

I have a requirement to hold employee information in hashmap with fields like empid, name, salary and fields like FL1, FL2 etc. So I am getting all these informations from database and putting into a hashmap as below

Then I put this map into the list and return back to the calling function. If there are 1200 emp i will have list size as 1200..i.e. 1200 map obj. In course of this process, there are chances that FL1..FL10 etc have some negative values which should be converted back to zero. I could handle that in the while loop when putting into map, but due to some other business logic, i should not convert into ZERO until the while loop finishes.

Now, as the list contains 1200..map objects and since i have to convert negative values in some fields of the maps to zero..i require to loop again..this will create an introduction of another big loop. Please let me know if you have any other thoughts to meet this scenario.